1. Field of the Invention
This invention relates to compositions classified in the art of chemistry as polymeric peroxides which are useful in the preparation of polycaprolactone block and graft copolymers, processes for their preparation and use and to intermediates for use in said processes, and to the use of said copolymers as compatibilizing agents for blends of immiscible polymers. More specifically, this invention relates to polycaprolactones end-capped with OO-t-alkylperoxy carbonate groups.
The blending of block copolymers with other polymers, in which the block components are compatible, is a well known method of compatibilizing blends of immiscible polymers. Poly(e-caprolactones) are compatible with a large number of commercial polymers, such as polypropylene, polyurethane, polyurea, poly(vinyl chloride), epoxy resins, polycarbonates, acrylonitrile-butadiene-styrene (ABS), styrene-acrylonitrile (SAN) and styrene-maleic anhydride copolymers (See D. R. Paul and S. Newman, eds., "Polymer Blends", Vol. 1, Chapter 2, Academic Press, New York, 1978). Consequently block copolymers of poly(e-caprolactones) have been found to be extremely useful as compatibilizing agents for a variety of polymer blends. They act as polymeric surfactants, lowering surface tension and promoting interfacial adhesion between the dispersed phase and the matrix phase in the polymer blend [N. G. Gaylord, J. Macromol. Sci.-Chem., A26(8), pp 1211-1229 (1989)].
However, all these block copolymers have been prepared by step-wise anionic polymerization of one monomer and then the other. This limits the variety of poly(e-caprolactone) block copolymers to those where the other polymer in the block copolymer can be prepared by anionic polymerization. There are some drawbacks to the anionic method of preparation. For example, in U.S. Pat. No. 4,603,171 it is reported that the alkyllithium-initiated polystyryl and polydienyl anions, or their corresponding oxyl-terminated anions, have been used to cross-initiate caprolactone polymerization. It further states that, "It has proved very difficult to channel the esterification reactions under the basic environment into the desired mode of selectivity to the exclusion of unzipping and scrambling transesterification as the side reactions compete with polyester formation. The depolyesterification due to intramolecular transesterification, e.g. unzipping or backbiting phenomena, produces cyclic ester oligomer contamination. Intermolecular transesterification (ester scrambling) generally results in uncontrolled molecular weight distribution."
The polymeric peroxides of this invention are capable of generating block copolymers with any free radical polymerizable monomer. Thus the variety of poly(e-caprolactone) block copolymers that may be commercially produced is broadened considerably. Likewise, the variety of polymer blends that can be compatibilized by poly(e-caprolactone) copolymers also increases.
2. Description of the Prior Art
Polymers containing peroxide groups are well known in the art. However, most of these peroxides have the peroxide groups in the polymer backbone and when the peroxide decomposes, the polymer backbone fragments.
The present patent disclosure is only concerned with polymeric peroxides where the peroxide groups are terminal groups so when they fragment, the poly(e-caprolactone) backbone remains intact and the free radicals generated on the polymer terminals can initiate polymerization and generate block copolymers.
U.S. Pat. Nos. 3,671,651 and 4,304,882 broadly disclose polymers with attached peroxide groups. These peroxy polymers were produced by the reaction of a peroxide containing an acylating agent, such as a haloformate or an acid halide group, and polymeric materials containing terminal or pendant hydroxyl, amino, mercapto or any other functional group that can be acylated. In general, U.S. Pat. No. 3,671,651 teaches that a peroxide with a discrete acylating functionality (i.e. the peroxide is separated from the acylating functionality by a 2-4 valent aliphatic, cycloaliphatic or aromatic diradical), such as an acid chloride or a chloroformate, can react with polymers containing terminal or pendant hydroxyl, amino, mercapto or any other functional group that can be acylated. The peroxides containing the acylating agents are difficult and somewhat dangerous to prepare and have not yet become commercial realities.
U.S. Pat. No. 3,671,651 specifically claims peroxy polymers in which the peroxide is attached to the polymer by either an ester or a carbonate group (i.e. connecting groups). Therefore, the peroxy polymers of U.S. Pat. No. 3,671,651 are outside the scope of this invention. U.S. Pat. No. 4,304,882 again teaches that peroxides with acylating functions can react with polymers containing terminal or pendant hydroxyl, amino or mercapto groups to form peroxy polymers. In the 4,304,882 patent, in addition to carbonate and ester linkages being claimed as connecting groups, amide and carbamate groups are also claimed as connecting groups linking the peroxide moiety to the polymer backbone. In neither patent is the peroxide group directly attached to the polymer backbone. In all cases the peroxide group is separated from the linking group by an aliphatic, cycloaliphatic or aromatic diradical. The patents specifically refer to prior art peroxy compounds containing acylating groups which fall outside the scope of U.S. Pat. No. 3,671,651 and U.S. Pat. No. 4,304,882 because the peroxy group is not separated from the acylating group and actually is a part of the acylating group. t-Alkylperoxy chloroformates were cited as examples of these prior art peroxides with acylating groups. Therefore, U.S. Pat. No. 3,671,651 and U.S. Pat. No. 4,304,882 actually were teaching away from the reaction of t-alkylperoxy chloroformates with polymers having terminal hydroxyl groups (which would provide the compounds of this invention by another synthetic route).
The polymeric materials disclosed in U.S. Pat. No. 4,304,882 were polyethers, polyesters, polyamides, polycarbonates, polybutadiene, polystyrene, poly(vinyl alcohol), partially hydrolyzed poly(vinyl acetate), cellulose, polybutadiene-polystyrene copolymer and any other polymeric material containing terminal or pendant groups selected from --OH, --NH.sub.2, --NHR or SH. Specifically U.S. Pat. No. 4,304,882 describes polyesters prepared from aliphatic, cycloaliphatic, aromatic and heterocyclic dibasic acids and dihydroxy compounds. No mention is made of polylactones.
U.S. Pat. No. 4,304,882 states that the peroxy polymers can be used in making graft and block copolymers by treating them with polymerizable vinyl-type monomers under conditions where the peroxy-carbon linkage is decomposed into free radicals at a rate and temperature suitable for polymerizing the vinyl monomer. These block and graft copolymers are useful as compatibilizing agents. It states that when block and/or graft copolymers of two incompatible homopolymers are present, the system becomes much more, if not completely, compatibilized. There is no mention of preparing poly(caprolactone) copolymers. U.S. Pat. No. 3,935,243 describes dialkyl alkylenebis-(peroxydicarbonates) and corresponding higher polyfunctional peroxydicarbonic acid esters. These compounds are prepared by reacting a sodium alkylperoxycarbonate with a diol bis(chloroformate) at from about -10.degree. C. to about 20.degree. C. The compounds have the general formula: ##STR1## wherein R.sup.1 is an alkyl radical of 1-6 carbon atoms, R is an alkylene radical of 2-8 carbons or a polyalkyleneoxy radical wherein each alkylene group has 2-4 carbon atoms and R has a maximum of about 12 carbon atoms and n is an integer, preferably 1-4.
Polymeric peroxydicarbonates were prepared by reacting the diol bis(chloroformate) with a mixture of a sodium alkylperoxycarbonate and sodium peroxide. ##STR2## The products are low temperature peroxides which are stable when stored below 12.degree. C. None of the diols used to prepare the bis(chloroformates) were polymeric or oligomeric diols. None of the diols were derived from caprolactone.
U.S. Pat. No. 3,523,920 teaches the crosslinking of polylactones with a free radical initiator to make the polylactones less sensitive to solvent attack and improve the softening points. The crosslinking agents were discrete free radical initiators that were added to the polylactones. None of the free radical initiators were attached to the polylactone chain.
European Patent EP 0,416,372 discloses peroxide terminated polycarbonates which are useful in the formation of copolymers which in turn are useful as compatibilizers for blends of polycarbonates with other polymers. The peroxide terminated polycarbonates are prepared by reacting dihydroxyaromatic compounds of formula EQU HO-A.sup.2 -Y-A.sup.3 -OH
and phosgene in the presence of a peroxy ester of formula ##STR3## as a chain terminating agent. A copolycarbonate is prepared by the reaction of a peroxide terminated polycarbonate with an ethylenically unsaturated compound, preferably a polymerizable monomer such as styrene, maleic anhydride and acrylonitrile.
U.S. Pat. No. 5,043,414 teaches the preparation of polycarbonates having terminal t-alkylperoxyformate groups. These peroxypolymers were prepared and then heated to high temperatures where the peroxy groups rearranged and decomposed in the presence of traces of water into hydroxy-terminated polycarbonates. The t-alkylperoxyformate terminated polycarbonates were prepared by the reaction of an aromatic dihydroxy compound, preferably a bisphenol, with phosgene in one or two steps, in the presence of a small amount of a t-alkyl hydroperoxide which was used as a chainstopper. They were not used as initiators of free radical polymerization or for grafting onto other polymers.
European Patent EP 0,418,913 A2 teaches the preparation of polymeric azo compounds by reacting condensation polymers containing functional groups with azo compounds containing co-reactive functional groups. The compounds were referred to as condensation polymer radical polymerization initiators. Since the condensation polymers were difunctional and the azo compounds were difunctional, polymers were obtained containing azo groups in the backbone. Examples were given where polycaprolactone was reacted with toluenediisocyanate to give polycaprolactone endcapped on both ends with isocyanate groups. The isocyanate functionalized caprolactone was then reacted with 2,2'-azobis[2-methyl-N(2-hydroxyethyl)propionamide] to form the polymeric azo compound. In a second example, the polymeric azo compound was prepared in 1 step by heating a mixture of polycaprolactone, 2,2'-azobis[2-methyl-N(2-hydroxyethyl)propionamide], diphenylmethanediisocyanate and a catalytic amount of stannous octoate. The polymeric azo compounds were decomposed in the presence of styrene to form a polycaprolactone-polystyrene block copolymer. The block copolymer was used as a low-profile additive in the curing of polyester resins.
U.S. Pat. No. 5,039,754 teaches polymeric peroxides containing a divalent recurring unit having the following formula: ##STR4## wherein the recurring unit has a 10 hour half life temperature of at least 80.degree. C. and R.sup.3 may be a polymeric radical of up to about 5,000. The polymeric peroxides are derived from the condensation polymerization of hydroxy-hydroperoxides and/or dihydroxy dialkylperoxides with difunctional co-reactants, such as phosgene, a bis-haloformate, a polyhaloformate, a diacid halide, a polyacid halide, a diisocyanate, a polyisocyanate and a dianhydride to form a peroxy-containing polymer. Suitable bis-chloroformates include the bis-chloroformates of polycaprolactone diols. In such a case the R.sup.3 divalent radical would have the following formula: ##STR5## These peroxy polymers were useful in preparing block copolymers. These compounds in contrast to the compounds of this invention fragment along the polymer backbone to form numerous radicals whereas the peroxy-terminated polymers of this invention only fragment at the end of the polymer chain. Consequently, essentially the total weight of the peroxy-terminated polymer of this invention, instead of just a fragment, is incorporated into the block copolymer.
C. Hepburn in Rubber World (Vol. 190 No. 2, pp 49-60, May 1984) reported on the use of bis(peroxycarbamates) as crosslinking agents for the vulcanization of rubber. A bis(peroxycarbamate) with a poly(e-caprolactone) backbone was prepared by reacting hydroxy-terminated poly(e-caprolactone) with an excess of isophorone diisocyanate end groups. The prepolymer was then reacted with 100% t-butyl hydroperoxide in the presence of triethylamine catalyst. The resulting polymeric bis(peroxycarbamate) was evaluated in the curing of natural rubber and isoprene rubber. It had a low curing efficiency and therefore was not evaluated any further. The polymeric bis(peroxycarbamate) is the only example to our knowledge of peroxy terminated poly(e-caprolactone).